Method for temperature control of a component

ABSTRACT

A method for temperature control of a component that is transferable between a first system and a second system includes: ascertaining a temperature drift of a temperature of the component that is to be expected after transfer of the component from the first system into the second system; and modifying a temperature prevailing in the first system and/or a temperature prevailing in the second system such that the temperature drift that is actually occurring after transfer of the component from the first system into the second system is reduced with respect to the expected temperature drift.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims benefit under35 USC 120 to, international application PCT/EP2018/077276, filed Oct.8, 2018, which claims benefit under 35 USC 119 of German Applications DE10 2017 219 151.1, filed on Oct. 25, 2017, and DE 10 2018 201 320.9,filed on Jan. 29, 2018. The entire disclosure of each of theseapplications is incorporated by reference herein.

FIELD

The disclosure relates to a method for temperature control of acomponent, wherein the component is transferable between a first systemand a second system. The disclosure is advantageously realizable inparticular in applications in which a temperature-sensitive component isintended to be regulated to a reference temperature that remains asconstant as possible or temperature drifts upon transferring thecomponent into different systems or compartments are intended to beavoided or at least reduced.

BACKGROUND

Microlithography is used for producing microstructured components suchas, for example, integrated circuits or LCDs. The microlithographyprocess is carried out in what is called a projection exposureapparatus, which includes an illumination device and a projection lens.The image of a mask (=reticle) illuminated by way of the illuminationdevice is in this case projected by way of the projection lens onto asubstrate (e.g. a silicon wafer) coated with a light-sensitive layer(photoresist) and arranged in the image plane of the projection lens, inorder to transfer the mask structure to the light-sensitive coating ofthe substrate.

In projection lenses designed for the EUV range, i.e. at wavelengths ofe.g. approximately 13 nm or approximately 7 nm, owing to the lack ofavailability of suitable light-transmissive refractive materials,mirrors are used as optical components for the imaging process.

In practice when employing replacement components e.g. in suchmeasurement methods, a great sensitivity of the measurement results withrespect to temperature changes exists, wherein a temperature control toa few millikelvin is desirable to achieve the desired measurementaccuracies. The realization of such exact temperature control, in turn,presents a demanding challenge in practice. One reason for this is thattypically, a replacement component used for a current measurementprocess is taken from a separate holder holding a plurality of differentreplacement components and transferred into the actual measurementsystem or a housing accommodating the measurement system, wherein acorresponding thermal adaptation of the relevant systems (holder on theone hand and measurement system on the other) is made more difficult bythe thermal loads which are present on both sides and possibly likewisesubject to temporal fluctuations.

In addition, after the transfer of the respective replacement componentinto the measurement system is complete, the approach thereof to arespective target temperature typically takes place over a time periodof several hours due to the relevant time constant, with the result thata comparatively long time period passes until a sufficiently hightemperature stability of the relevant replacement component is attained.

An insufficient temperature stability of the replacement component,however, results in undesired changes in the optical properties, such asthermally induced refractive index variations and mechanical drifteffects in the measurement setup and consequently ultimately errors inthe measurement.

In practice, impairments of the temperature stability of the replacementcomponent and associated issues can furthermore result from the factthat the replacement component is typically also exposed to thermalloads during its transfer into the measurement system (i.e. on its waythere). Such thermal loads can originate from motors that are usedmerely by way of example for the transfer (and which may be arrangede.g. at a gripper or robot arm used for handling the replacementcomponent), but also from other components in the environment of therespective transport path. Here, the change in the thermal state of thereplacement component that has been caused by the relevant thermal loadscan include heating and/or cooling, wherein these effects can alsovaryingly occur over the entire volume of the replacement component,depending on the relative position of the thermal loads.

Regarding known technology, reference is only made by way of example toEP 1 531 364 B1.

SUMMARY

The present disclosure seeks to provide a method for temperature controlof a component, wherein temperature drifts are reduced during thetransfer of the component between a first system and a second system andassociated issues are at least largely reduced.

According to one aspect, a method according to the disclosure fortemperature control of a component, wherein the component istransferable between a first system and a second system, includes thefollowing steps:

-   -   ascertaining a temperature drift of a temperature of the        component that is to be expected after transfer of the component        from the first system into the second system; and    -   modifying a temperature prevailing in the first system and/or        temperature prevailing in the second system such that the        temperature drift that is actually occurring after transfer of        the component from the first system into the second system is        reduced with respect to the expected temperature drift.

For temperature control of a component which is transferable between afirst and a second system, the disclosure is here in particular based onthe concept, for example, not of actuating both systems by specifyingidentical predetermined temperature values (that is to say e.g.supplying cooling water of the same temperature to cooling apparatuseswhich are respectively assigned to the systems), but, first,ascertaining the temperature drift (or temporal variation of temperatureor temperature change) that is to be expected after transfer of thecomponent from the first system into the second system and modifying onthat basis the temperature in at least one of the two systems.

Various strategies are possible both according to the disclosure withrespect to the ascertainment of the expected temperature drift and alsothe subsequent modification of the temperature prevailing in the firstsystem and/or the second system, as will be explained in more detailbelow.

In accordance with an embodiment, the temperature measurements using asensor that is attached to the component can be performed before and/orafter the transfer of the component from the first system into thesecond system. Alternatively or additionally, it is also possible for atemperature that is currently prevailing in the first system and/or fora temperature that is currently prevailing in the second system to bemeasured. Furthermore, a predictive model can be established forpredicting a development of the temperature of the component over timeafter the component has been transferred from the first system into thesecond system (possibly also in combination with the aforementionedembodiments).

As far as the step of modifying a temperature prevailing in the firstsystem and/or a temperature prevailing in the second system isconcerned, this step can be effected by way of modifying thepredetermined value of a corresponding temperature regulation, andalternatively or additionally also by way of modifying the operation ofat least one structural element that is present in the first systemand/or in the second system (with corresponding change in the relevantthermal load).

According to an embodiment, the method further includes the steps of:

-   -   ascertaining a change in the thermal state of the component that        is to be expected on the way from the first system to the second        system; and    -   performing temperature control of the component before it is        transferred into the second system in a manner such that the        expected change is at least partially compensated.

The disclosure furthermore relates to a method for temperature controlof a component, wherein the component is transferable between a firstsystem and a second system, wherein the method includes the followingsteps:

-   -   ascertaining a change in the thermal state of the component that        is to be expected on the way from the first system to the second        system; and    -   performing temperature control of the component before it is        transferred to the second system in a manner such that the        expected change is at least partially compensated.

In accordance with an embodiment, the component is transferred into aregion which is separate from at least one further component present inthe first system before the temperature control.

In accordance with an embodiment, the ascertainment of a change of thethermal state of the component that is to be expected on the way fromthe first system to the second system is effected by simulating and/ormeasuring the influence of thermal loads to which the component isexposed on the way from the first system to the second system.

In embodiments of the disclosure, the component includes an opticalcomponent, in particular an optical replacement component that isadapted to a test specimen geometry. The wording “adaptation to a testspecimen geometry” should be understood here in particular to mean that,for example in the case of a compensation optical unit, the relevant(optical replacement) component is also replaced when the test specimenis replaced or a test specimen having a different geometry or topographyis to be measured. For example, the optical replacement component can bea calibration mirror, wherein, depending on the test specimen to bemeasured, calibration mirrors having different radii of curvature anddiameters are swapped for one another.

However, the disclosure is not limited hereto, but is also in principleadvantageously realizable in other applications in which atemperature-sensitive component is intended to be regulated to areference temperature that remains as constant as possible or theproblem of temperature drifts upon transferring the component intodifferent systems or compartments is intended to be avoided or at leastreduced.

In accordance with an embodiment, the component is a lithography mask.The first system can be a holder for storing a plurality of lithographymasks. The second system can be a mask metrology apparatus, which can beused for characterizing structures on the mask with regard to deviationsof the respective structure from the nominal/desired position(“registration”) and/or with regard to the critical dimension (CD) ofthe respective structures.

Further configurations of the disclosure can be gathered from thedescription and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is explained in greater detail below on the basis ofexemplary embodiments illustrated in the accompanying figures, in which:

FIGS. 1-5 show schematic illustrations for explaining exemplaryembodiments of the present disclosure; and

FIG. 6 shows a schematic illustration of a projection exposure apparatusdesigned for operation in the EUV.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

To start, FIG. 6 shows a schematic illustration of a projection exposureapparatus that is given by way of example and is designed for operationin the EUV range.

According to FIG. 6, an illumination device in a projection exposureapparatus 10 designed for EUV includes a field facet mirror 3 and apupil facet mirror 4. The light from a light source unit including aplasma light source 1 and a collector mirror 2 is directed onto thefield facet mirror 3. A first telescope mirror 5 and a second telescopemirror 6 are arranged in the light path downstream of the pupil facetmirror 4. A deflection mirror 7 is arranged downstream in the lightpath, the deflection mirror directing the radiation that is incidentthereon onto an object field in the object plane of a projection lensincluding six mirrors 21-26. At the location of the object field, areflective structure-bearing mask 31 is arranged on a mask stage 30, themask being imaged with the aid of the projection lens into an imageplane in which a substrate 41 coated with a light-sensitive layer(photoresist) is situated on a wafer stage 40.

The mirror that is tested within the scope of the disclosure can be e.g.any mirror of the projection exposure apparatus 10, for example themirrors 21 or 22 of the projection lens, or else the mirror 7 of theillumination device.

FIG. 1 shows merely a schematic illustration to illustrate a possiblescenario in which the method according to the disclosure can berealized.

In this exemplary embodiment, a component 131 which is to betemperature-controlled in accordance with the disclosure is an opticalreplacement component which is adapted to the test specimen geometry. Inaccordance with FIG. 1, this component is arranged with a plurality offurther components (of which for the sake of simplicity merely twocomponents 132 and 133 are shown) in a holder 110. “120” denotes ameasurement arrangement (accommodated in a corresponding housing 121)for testing a mirror, in particular a mirror of a microlithographicprojection exposure apparatus. “140” denotes thermal loads, which aremerely indicated, both in the holder that forms the first system 110 andin the measurement arrangement that forms the second system 120. As isindicated by the double-headed arrow in FIG. 1, in each case one of thecomponents 131, 132, 133, . . . is transferred into the measurementarrangement, or the second system 120, for use for an interferometricmeasurement.

For keeping temperature drift effects, and associated impairments of themeasurement accuracy, as low as possible during the interferometricmeasurement here, various embodiments will be described below. Whatthese embodiments have in common is not that, for example, both systems110, 120 are regulated from the start merely to the same predeterminedtemperature value, but rather, first, a temperature drift (or temporalvariation of temperature or temperature change) that is to be expectedafter transfer of the respective component from the first system 110into the second system 120 is ascertained and subsequently a temperatureprevailing in the first system 110 and/or a temperature prevailing inthe second system 120 is modified in dependence on the expectedtemperature drift.

In accordance with a first embodiment (described in the flowchart ofFIG. 2), a temperature sensor can be attached directly to the relevantcomponent 131 (or 132, 133, . . . ), by way of which sensor acorresponding temperature offset value is obtained with correspondingtemperature measurements before or after transfer of the component fromthe first system 110 into the second system 120 (steps S21 and S22). Thetemperature offset value in turn can be used as the basis for themodification of the temperature prevailing in the first system 110 orthe second system 120 (step S23). As far as the latterly mentionedmodification of the temperature in the first system 110 and/or thesecond system 120 is concerned, the modification can include modifyingthe predetermined value of a corresponding temperature regulation and/ormodifying the operation of at least one structural element present inthe relevant system (i.e. the change in a corresponding thermal load).

In accordance with a further embodiment (described in the flowchart ofFIG. 3), the ascertainment of the temperature drift of the component 131(or 132, 133, . . . ) that is to be expected after transfer of therelevant component 131 from the first system 110 into the second system120 can also be effected using positionally fixed temperature sensors(denoted with “150” in FIG. 1) which are present in the respectivesystem 110 or 120, with the result that the temperature that iscurrently prevailing in the first system 110 and the temperature that iscurrently prevailing in the second system 120 can be measured in eachcase (steps S31 and S32). Based on these measurements, which in furtherembodiments can also be performed in combination with temperaturemeasurements using a sensor that is attached to the respectivecomponent, in accordance with FIG. 2, the temperature prevailing in thefirst system 110 and/or in the second system 120 is again modified asdescribed above.

In a further embodiment (which can be realized again in combination withone or both of the embodiments that have been described above withreference to FIG. 2 and FIG. 3), a predictive model is establishedaccording to the disclosure (as described in the flowchart of FIG. 4)for predicting a development of the temperature of the relevantcomponent 131 (or 132, 133, . . . ) over time after the transfer fromthe first system 110 into the second system 120 (step S41), wherein thispredictive model is again used as the basis for the modification,performed as has already been described above, of the temperatureprevailing in the first system 110 and/or in the second system 120 (stepS42).

The predictive model can be established on the basis of experimentaldata (e.g. with respect to the behaviour of the measurement arrangementover time or of the housing accommodating the latter in dependence onthe measurements performed with the measurement arrangement) and/or onthe basis of theoretical analyses. In this case, measurement signals offurther sensors e.g. with respect to the temperature in the environmentor in the clean room and/or the temperature of the housing wall or ofthe housing accommodating the measurement arrangement may be taken intoaccount during the establishment of the model. Furthermore, it ispossible when establishing the model to take account of the fact thatdifferent positions of the components in the first system, or holder,could result in different offset values after transfer of the componentfrom the first system 110 into the second system 120 due to the varyingproximity with respect to the existing thermal loads. In this way it ispossible for example to always perform a modification of the temperaturein the first system taking place subsequently in the method according tothe disclosure exactly in a manner such that a temperature drift isreduced or minimized for the respective component that is to betransferred next into the second system.

In a further embodiment, the above-described embodiments or steps canalso be combined as follows:

At a first stage, a corresponding temperature offset value can bedetermined, analogously to FIG. 2, with corresponding temperaturemeasurements using a temperature sensor that is attached directly to therelevant component 131 (or 132, 133, . . . ) before or after transfer ofthe component 131 from the first system 110 into the second system 120(steps S21 and S22), whereupon a (first) modification of the temperatureprevailing in the first system 110 or the second system 120 (step S23)is performed.

Next, the temperature of the relevant component 131, which has beentransferred into the second system 120, can continue to be measured ormonitored using the temperature sensor that is attached to the component131 and be used as the basis for a continuous adaptation of thetemperature prevailing in the first system 120. It is also possible hereto take account of any temperature changes that can occur on arelatively short time scale, which take place in the first and/or secondsystem and can be ascertained in accordance with FIG. 3 (steps S31 andS32).

Finally it is possible, on the basis of the data obtained in theprevious steps—and any further data relating to measurement activitiesof the measurement arrangement—to establish a predictive model, whereinthe further development of the temperature of a (replacement) componentthat is currently used or will be used in future in the measurementarrangement over time can be predicted using the model and be used as abasis for modifying the temperature prevailing in the first system 110and/or in the second system 120.

In a further embodiment, which will be described below with reference toFIG. 5 and is realizable both in combination with and independently fromthe above-described embodiments, it is also possible according to thedisclosure to take account of thermal loads to which the component 131is exposed during the transfer into the second system 120 (i.e. on theway there). These may be, merely by way of example, thermal loads thatoriginate from a motor that is located on a gripper arm used fortransferring the component 131. Furthermore, the lights may also be anyother thermal loads to which the component 131 is temporarily exposed onthe way into the second system 120.

According to FIG. 5, in a first step S51, a thermal change that is to beexpected during the transfer of the component 131 from the first system110 to the second system 120 is first ascertained. This ascertainmentcan also be performed—with a corresponding knowledge of the relevantthermal loads—as part of a simulation or in a prior measurement orcalibration.

In the case of the ascertainment by way of measurement or calibration,it is possible to transfer from the first system 110 to the secondsystem 120 not the component 131 but first a calibration component,wherein it is possible to measure the heating or cooling in a spatiallyresolved fashion by way of suitable temperature sensors that areprovided (e.g. at the calibration component itself or a correspondingmount).

According to FIG. 5, the component 131 which is still located in thefirst system 110 is transferred, in an optional further step S52, intoanother region which is located further away from the remainingcomponents 132, 133, . . . in the first system so as to avoid undesiredthermal influencing or disturbance of the components 132, 133, . . . ,wherein the other region can be located either likewise in the firstsystem 110 or outside it.

Subsequently, in step S53, temperature control of the component 131 isperformed to compensate the thermal change that was ascertained in stepS51 and is to be expected during the transfer into the second system120. For this purpose, merely by way of example, one or more heating orcooling elements can be used (e.g. heating or cooling plates, Peltierelements etc.), which can be moved e.g. into the surrounding area of thecomponent 131 or be already present there. The heating or coolingelements can also be used to perform, in spatially resolved fashion(i.e. varying over the surface or the volume of the component 131),heating or cooling of the component 131. Likewise optionally, one ormore heat shields can be moved into the region between component 131 andthe remaining components 132, 133, . . . in the first system 110 tofurther minimize thermal influencing or disturbance of the remainingcomponents 132, 133, . . . .

In the case of a locally limited temperature control of the component131 (which is intended to take account of e.g. a locally limited heatingor cooling of the component 131 that is to be expected on the way to thesecond system 120), which is desired in step S53, the temperaturecontrol is preferably performed in step S53 only immediately before thebegin of the transfer to the second system 120 in order to avoid atemperature equalization within the component 131 which may otherwiseoccur in the meantime due to thermal conduction.

Finally, in step S54, the component 131 is transferred into the secondsystem 120. With a suitable temperature control of the component 131,which previously took place in step S53, the component 131 at the end ofthis transfer process, i.e. at the point of time where the component 131is placed in the second system 120, reaches exactly the temperature thatis desired there, i.e. the thermal loads which act on the component 131during the transfer on the way between the first system 110 and thesecond system 120 precisely cancel each other out with the temperaturecontrol which was performed for compensation purposes in step S53.

Even though the disclosure has been described on the basis of specificembodiments, numerous variations and alternative embodiments areapparent to a person skilled in the art, for example by combinationand/or exchange of features of individual embodiments. Accordingly, itgoes without saying for the person skilled in the art that suchvariations and alternative embodiments are concomitantly encompassed bythe present disclosure, and the scope of the disclosure is restrictedonly within the meaning of the appended patent claims and theequivalents thereof.

What is claimed is:
 1. A method of modifying a temperature of an optical replacement component that is adapted to a test specimen geometry, the method comprising: a) determining an expected drift of a temperature of the optical replacement component due to transferring the optical replacement component from a first system to a second system; and b) modifying a temperature prevailing in the first system and/or a temperature prevailing in the second system so that an actual drift of the temperature of the optical replacement component after transferring the optical replacement component from the first system to the second system is reduced compared to the expected temperature drift determined in a).
 2. The method of claim 1, wherein a) comprises measuring a temperature that is currently prevailing in the first system and/or measuring a temperature that is currently prevailing in the second system.
 3. The method of claim 1, further comprising performing temperature measurements using a sensor attached to the optical replacement component before and/or after transferring the optical replacement component from the first system to the second system.
 4. The method of claim 1, further comprising establishing a model to predict a development of the temperature of the optical replacement component over time after transferring the optical replacement component from the first system to the second system.
 5. The method of claim 1, further comprising modifying a predetermined value of a temperature regulation present in the first system and/or in the second system.
 6. The method of claim 1, wherein b) comprises modifying operation of as structural element disposed in the first system and/or in the second system.
 7. The method of claim 1, further comprising: determining an expected change in a thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system; and before transferring the optical replacement component to the second system, modifying the temperature of the optical replacement component to at least partially compensate the expected change in the thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system.
 8. The method of claim 7, further comprising, before modifying the temperature of the optical replacement component to at least partially compensate the expected change in the thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system, transferring the optical replacement component into a region which is separate from at least one further component present in the first system.
 9. The method of claim 7, wherein determining the expected change in a thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system comprises simulating and/or measuring an influence of thermal loads to which the optical replacement component is exposed during transfer of the optical replacement component from the first system to the second system.
 10. The method of claim 1, wherein the optical replacement component comprises a calibration mirror comprising a mirror curvature adapted to the test specimen geometry, and/or the optical replacement component comprises a calibration mirror comprising a mirror diameter adapted to the test specimen geometry.
 11. The method of claim 1, wherein the first system comprises a holder configured to store a plurality of optical replacement components.
 12. The method of claim 1, wherein the second system comprises a measurement arrangement configured to test a mirror of a microlithographic projection exposure apparatus.
 13. The method of claim 1, wherein the optical replacement component comprises a lithography mask.
 14. A method of modifying a temperature of an optical replacement component that is adapted to a test specimen geometry, the method comprising: determining an expected change in a thermal state of the optical replacement component during transfer of the optical replacement component from a first system to a second system; and before transferring the optical replacement component to the second system, modifying a temperature of the optical replacement component to at least partially compensate the expected change in the thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system.
 15. The method of claim 14, further comprising, before modifying the temperature of the optical replacement component to at least partially compensate the expected change in the thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system, transferring the optical replacement component into a region which is separate from at least one further component present in the first system.
 16. The method of claim 14, wherein determining the expected change in a thermal state of the optical replacement component during transfer of the optical replacement component from the first system to the second system comprises simulating and/or measuring an influence of thermal loads to which the optical replacement component is exposed during transfer of the optical replacement component from the first system to the second system.
 17. The method of claim 14, wherein the optical replacement component comprises a calibration mirror comprising a mirror curvature adapted to the test specimen geometry, and/or the optical replacement component comprises a calibration mirror comprising a mirror diameter adapted to the test specimen geometry.
 18. The method of claim 14, wherein the first system comprises a holder configured to store a plurality of optical replacement components.
 19. The method of claim 14, wherein the second system comprises a measurement arrangement configured to test a mirror of a microlithographic projection exposure apparatus.
 20. The method of claim 14, wherein the optical replacement component comprises a lithography mask. 